Human motion requires exertion of energy. Peoples' ability to conduct their activities can be limited by their available energy, more specifically metabolic energy. For example, hikers have a limit to the distance they can hike based upon their physiological constitution and condition. Runners have a limit to the speed they can run. Military troops have a limit to the distance they can march, for example, with a heavy pack load. Athletes have a limit of how long they can remain within a physiological envelope of control that allows them to maintain adequate resilience to injury. People often seek ways to extend their capabilities—to run faster, hike farther, jump higher, stay more resilient, etc. It would be desirable to extend people's capabilities and overcome some of their limitations.
It is known generally that a device can receive a force and store potential energy. Later, the device may be actuated to release the potential energy as kinetic energy. During dorsiflexion motion of the ankle system, a stored potential energy may be returned as force during plantar flexion motion. It is broadly known that the Achilles tendon acts in this way. With the assistance of such force and energy, a person is less dependent upon internal muscles, flexor tendons and tendons for locomotion and stability. The person can perform better, require less consumption of metabolic energy, produce less blood-born byproducts of muscular exertion, experience less fatigue and be able to maintain an envelope of control which provides sustained resilience to injury, recuperate from lower limb issues faster and receive other health and performance benefits.
Gait Cycle
Human locomotion is driven by three major energy sources—the foot system, the knee system and the hip system. Each of these systems is moved by a combination of muscle force as well as tendon force. In a typical walking gait, roughly 40 to 45% of energy is provided by the foot system, which surpasses the individual contributions of both the knee and hip systems. As stride length or gait speed increases the relative contribution of the foot system decreases in relation to the knee and hip system.
During a gait cycle, as the term is used herein, the Achilles tendon stretches during dorsiflexion motion and releases during plantar flexion motion. The efficiency of the Achilles tendon is quite high, with laboratory measures showing a potential for a greater than 90% energy return. The Achilles is defined herein as an elastomeric element that is capable of stretching up to 8% of total length under load before plastic deformation.
The use of powered exo-skeletons has been demonstrated in the laboratory; (reference may be made to articles cited in the attached bibliography, incorporated by reference herein as to any material deemed essential to an understanding of the principles of energy management, injury reduction or injury rehabilitation disclosed herein). The use of powered exoskeletons for the ankles has been tested on a treadmill and shown to potentially enable improved performance. These studies also show that managing the timing of the release of energy from these powered systems requires learning on the part of the wearer. Proper control of muscular exertion by the wearer to achieve harmonization of the device with the gait cycle is a necessity for a person to gain significant benefit.
Because of these tests, supplementing the foot system with support and added energy capability through an external system can be hypothesized as meaningful and significant. A supplemental system can help athletes perform better. Such a system can help boost walking endurance; it can help people with ankle and Achilles tendon injuries recuperate faster and help avoid future problems. Also, it can help people walk more easily and with less fatigue, which may be of significant value in places where people walk long distances to work, to gather food or water, etc. Such a system should also be timed correctly to harmonize with the proper need for energy.
Plane of Reference
Performance benefits that may be achievable using a system as described herein include improved speed, improved endurance, increased jump height, increased backpack loading, decrease in oxygen consumption, etc. A focus of such a system may be on the rotation of the ankle joint in the sagittal plane as a main source of force and energy.
Benefits may also be achieved by using a system as described herein in the frontal plane. In shoe structural design, the frontal plane may be utilized to maintain or extend a shoe's protective capabilities in the ankle and limit range of untoward motion in the ankle that may otherwise lead to soft tissue injury, joint injury or other injuries. The system as described herein has shown unexpected benefits during clinical testing in managing foot-fall, reducing shuffling of feet and improved directional consistency in how toes are pointed, which may all be considered novel benefits measured during frontal plane analysis. The system as described also constrains the degrees of freedom for ankle motion, which further provides protective qualities toward injury reduction or rehabilitation.
Systems and preferred aspects disclosed herein integrate with items that are commonly worn on the body. This comprises footwear, which may refer to any variety of shoes, boots, sneakers, sandals or other article of wear that is worn upon the foot, and body wear, which may refer to any variety of pants, sporting uniforms, military uniforms, sock, hosiery, ankle guard, shin guards, combat protective leg wear, orthosis or other item which is donned upon at least upon the lower limbs.
Typical Biomechanics of the Human Ankle
A typical human ankle range of motion is commonly discussed in biomechanics literature with variations according to each authors' clinical experience; the following overview of the normal gait cycle is a simplified recounting of common literature.
The gait cycle may begin with the first touch of the foot to the ground. This first touch begins the cycle at 0% and the moment immediately prior to the following touch to the ground of the same limb may represent 100% of a cycle. In the normal walking gait, the ankle may experience a small amount of extension after initial contact leading to plantar flexion during the first 10-15 or so percent of the cycle, commonly referred to as a loading response. This is then followed by increasing amounts of dorsiflexion motion, which further increases after mid-stance. Maximum dorsiflexion is typically achieved after heel lift and prior to the initial contact of the opposite foot. This is followed by rapid plantar flexion motion associated with push off, which occurs after the opposite foot makes its initial contact. In the push-off phase, the ankle rapidly plantar flexes through toe off. This is followed by a swing phase with the foot traveling in the air. During the swing phase, the foot dorsiflexes to a neutral position preparing it for the next cycle.
For simplicity in writing of this disclosure, we will refer to ankle system motion during the periods of increasing flexion after initial contract and loading response, through mid-stance, through heel lift, to peak dorsiflexion as “dorsiflexion”; and we will refer to ankle system motion during the periods of increasing extension found during opposite foot contact through toe off as “plantar flexion”.
The total range of motion in the ankle during a walking gait is the result of a combination of dorsiflexion angle and plantar flexion angle. After midstance, there is increasing dorsiflexion to a peak of 5 to 15 degrees as measured according to well known technical arts. During push off, the ankle rapidly plantar flexes to a peak of −5 to −20 degrees. Typical total range of motion during the normal walking gait is often shown as 20 to 40 degrees in common literature and internet resources.
Analyzing the running gait where a walking gait has been discussed above, we see similar elements of the cycle; however, efficient runners may not land on their heels in order to prevent unnecessary losses in energy. Rather, initial contact may be on the front part of the foot while the ankle is in slight dorsiflexion. The amount of dorsiflexion increases after midstance to a peak of 20 to 50 degrees. This is followed by rapid and powerful push off during which the ankle plantar flexes to a peak of −10 to 30 degrees. This results in a total range of motion of 40 to 70 degrees. Jogging gaits may range between the walk and run depending upon the person jogging, their abilities, the conditions, their level of exertion, etc. Sprinting gaits often show a decrease in range of motion when the athlete is near the top of their speed range.
Benefits of External Assistance During Dorsiflexion
When an ankle is in dorsiflexion phase, with a joint angle greater than zero, some amount of force needs to be applied to keep the ankle joint angle from rapidly increasing which would lead to the joint collapsing under the weight of the body. This is sometimes referred to as negative work. The removal or full rupture of the Achilles tendon and removal of other supportive ankle muscles & tendons, for example, during this phase would result in joint instability and the inability for a person to bear their body weight upon that foot. Any amount of dorsiflexion results in a necessary force being exerted in the ankle region to prevent joint collapse. A reduction in the force necessary to support the body during dorsiflexion phase, therefore, can be perceived as a potential opportunity to save energy or boost performance. Negative work consumes metabolic energy, and the reduction of negative work can reduce metabolic energy consumption. The reduction in metabolic consumption based upon the externalization of forces is asserted to increase as the vertical travel of the body's center of mass increases and speed of gait increase.